Switch to .NET 4.0.
Merge pull request #112 from SubtitleEdit/net-4

Switch to .NET 4.0.
Updated change log
Save overwrite checkboxes in Tools -> Batch convert - thx XhmikosR :)
NHunspell .net dll recompiled to .NET Framework 4
Merge branch 'master' of https://github.com/SubtitleEdit/subtitleedit
updated with upstream master